The IP-based IMT (International Mobile Telecommunication) network platform (IP2 from now on) is a network architecture that supports terminal mobility with both route optimization and location privacy [T. Okagawa, M. Jo, K. Nishida, A. Miura, “IP Packet Routing Mechanism Based on Mobility Management in IP-based IMT Network Platform,” ICIN 2003, March 2003.] Fundamental to IP2 is the separation of the Network Control Platform (NCPF) and the IP Backbone (IP-BB). The NCPF controls the IP-BB. The IP-BB comprises IP routers with additional packet processing features, such as address switching. The NCPF comprises signaling servers that command the IP-BE entities intelligently.
Mobile terminals (or mobile nodes, MN) are assigned permanent terminal identifiers that take the form of an IP address. In addition MNs are assigned a routing address by the IP2 access router (IP2AR). In basic IP2 the mobile terminal is attached to an IP2AR. The routing address is specific to the location of the MN, and to support location privacy it shall not be revealed to any other MNs. When the MN moves to another IP2AR, a new routing address is allocated to the MN from the pool of routing addresses available at the new IP2AR. The binding between the MN's terminal identifier (IPha, as of “IP home address”) and its routing address (IPra, as of “IP routing address”) is communicated to the NCPF by the IP2AR.
When a MN (MN1) wishes to send a packet to another MN (MN2) it uses MN2's IPha as destination address in the packet and transmits the packet to its IP2AR (IP2AR2). IP2AR1 (defined as the sending IP2AR) detects that the packet is addressed to an IP2 MN and queries the NCPF about the location of MN2. The NCPF responds with the IPra of MN2, stored in AR1, along with the IPha of MN2. Then, the destination address of the packet (IPha of MN2) is replaced to the IPra of MN2. This operation is referred to as address switching (optionally, the source address of the packet can also be replaced to the IPra of MN1). The packet is then delivered using traditional IP forwarding to the node that owns the IPra of MN2. The node is IP2AR2. IP2AR2 (defined as the receiving IP2AR) then replaces the destination (and optionally the source) address of the packet to the IPha of MN2 and delivers the packet to MN2.
An important function of IP2 is IP2AR notification. Whenever MN2 moves to a new IP2AR (probably as a result of IP handover), the new IP2AR allocates a new IPra for MN2 and the NCPF is updated with this new IPra. Then the NCPF notifies all IP2ARs that have MNs that send packets to MN2. As a result, sender IP2ARs will send MN2's packets to the new location.
FIG. 1 shows a basic Mobile IP system. Mobile IP version 6 (MIP from now on) is an Internet Engineering Task Force (IETF) defined method for handling IP node mobility [D. Johnson, et al, “RFC 3775: Mobility Support in IPv6”, June 2004, IETF]. All MIP aware MNs have a Home Agent (HA) and a permanent Home IP Address. The Home IP Address is topologically correct at (i.e., routed towards) the HA. From the MN's perspective this address is similar to the IPha defined in the IP2. Both addresses are unique and permanent identifiers of the given MN. From now on, the term IPha will be also referred to as the MIP Home IP Address of the terminal.
An IP subnet, to which a MN can be attached, will be referred as a “Visited Network” (VN). The MN's HA is located outside of any possible VNs. When an MN is located in a VN the MN cannot use its IPha as a valid IP address since the IPha is topologically incorrect within the VN. For this reason, the MN configures a Care of Address (CoA) using a valid local prefix. The CoA can be used to send and receive IP packets as long as the MN stays in the same visited IP network. Changing the VN will result in IP handover. The term Correspondent Node (CN) is used to denote the IP host that the MN is communicating with. One MN may have multiple CNs at the same time, and CNs can themselves be mobile.
A MIP enabled MN can choose between two kinds of communication forms to maintain session continuity in case of IP mobility. In the first case all traffic between the CN and the MN is sent through the HA using bi-directional tunneling. The MN updates its HA whenever the MN's CoA has been changed using Binding Update (BU) messages. The HA tunnels all IP packets arrived to the MN's IPha using the MN's actual CoA. Similarly, the MN tunnels all its transmitted packets to the HA, using IPha as the inner source IP address. The HA decapsulates the packets and transmits them towards their ultimate destination. This form of communication enables location privacy if the HA is trusted by the MN. However, one drawback of this mode of communication is route sub-optimality: all packets need to, go through the Home Agent.
The second way of communication in MIP is route optimization. Route optimization enables packets to travel between the MN and the CN directly without visiting the HA. It is performed in an end-to-end fashion by directly transmitting BUs between the MN and the CN. This action breaks location privacy since the location of a MN (the CoA, which is topologically specific) is revealed to the CN.
Route optimization (second case) in MIP is done in an end-to-end fashion. The MN enables route optimization by sending a BU message to its CN. This BU message contains MN's CoA. From this point a NIP aware CN and MN can directly exchange IP packets using the CoA as source or destination address and putting the MN's IPha as a Home Address Option into the IP headers in order to identify the MN. Such packets are sent using the optimal route.
FIG. 2 shows a Hierarchical Mobile IP system. Hierarchical Mobile IP (HMIP) [H. Soliman, et al, “Hierarchical Mobile IPv6 mobility management (HMIPv6)”, 16 Jun. 2004, IETF Draft] introduces a Mobility Anchor Point (MAP), which serves as “local” HA, adding a new hierarchy level to the MIP system. MNs exact point of attachment to the IP network is characterized by a CoA configured at its current link. This IP address is referred to as the Local Care-of-Address (LCoA). HMIP aware MNs can update their MAPs using the LCoA in case of IP handovers. This is beneficial when the MAP is topologically close to the moving MN and its HA and the CNs are far away. In this case, a Regional Care-of-Address (RCoA) is configured at the MAP and used instead of the LCoA for those nodes (i.e., the HA and CNs), which are far away from the MN. All IP handovers “under” the same MAP are not visible to nodes if the MN uses its RCoA as a CoA. Additionally the CNs cannot learn the exact location of the MN, but the approximate location is revealed via the RCoA.